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Re: JFC-Bloodiest Battle ??



Scott wote:

"but inventing a niche that does not currently exist is an extraordinary claim, and requires comensurate levels of evidence."

What, pray tell, is the modern day niche equivalent of therezinosauroids and Mononykus and its relatives?

Dan


dinoboygraphics@aol.com wrote:
My point is that the default should not be active predation -- other
options are viable, even if it is difficult to distinguish between them morphologically. <<<

Sorry, I have to disagree with Dan. In the absence of any terrestrial carnivores that are not active predators, the burden of evidence has to be on advocates to show that it's even energetically possible. Of course it's entirely possible that dinosaurs (or other extinct organisms) filled niches that are empty today, but inventing a niche that does not currently exist is an extraordinary claim, and requires comensurate levels of evidence. Furthermore, if support for such a niche is possible, then we would need to evaluate osteological correlates on a species by species basis.

Given the excellent finite-element analysis done on allosaur skulls, whose interpretted slash and rake attack style has been corroborated by recent phylogenetically constrained muscle restorations, there seems little reason to speculate that allosaurs filled an ecological niche that does not exist in current ecosystems.

Scott

Scott Hartman
Science Director
Wyoming Dinosaur Center
110 Carter Ranch Rd.
Thermopolis, WY 82443
(800) 455-3466 ext. 230
Cell: (307) 921-8333

www.skeletaldrawing.com


-----Original Message----- From: Dan Chure <danchure@easilink.com> To: habib@jhmi.edu Cc: DML <dinosaur@usc.edu> Sent: Fri, 22 Aug 2008 2:44 pm Subject: Re: JFC-Bloodiest Battle ??


0AMike; I agree. I admit it is arm waving. My point is that the default should not be active predation -- other options are viable, even if it is difficult to distinguish between them morphologically. Varanoids have low wide skulls, crudely like that of crocodilians (for the sake of this argument). Allosaurus and a number of other large headed theropods have extremely narrow preorbital regions, quite in contrast to varanoids. Take a look at the dorsal view of the skull of Monolophosaurus or Sinraptor. While vertical loads might be accommodated, I am less certain about resistance to torque along the long axis of the preorbital region, especially given all the pneumatic penetration of the region. Given the lack of similarity between theropods and living terrestrial vertebrates, it would not surprise me that they are making livings in ways unlike anything around now, including a life based primarily on scavenging. As Peter Dodson once wrote "let dinosaurs be dinosaurs." Dan Mike Habib wrote:
Allosaurus, like Sinraptor and Monolophosaurus, has an exceedingly
>> narrow preorbital region. All three are like a pair of scissors and >> quite unlike Tyrannosaurus with arched and fused nasals. I doubt >> Allosaurus was capable of sustaining great stresses, especially given >> the extensive pneumatic system enclosed in the narrow skull. Given >> the abundance of Morrison sauropo
ds, Allosaurus might have been >> primarily a scavenger, rather than a predator, although that is >> pretty much am waving. Jurassic Scavenger Club anyone?
An open skull construction need not mean that the maximum loads are >
low - depending on the particular strain distribution, a kinetic skull > can often take fairly substantial loads without failure. A more > heavily built skull may indeed be stronger still, but I would be > hesitant to assume that a more open, mobile skull morphology entails > carrion feeding. Varanids, for example, have a very open skull > construction, with a high degree of cranial kinesis, and yet are > active predators of a range of prey items.
Cheers, --Mike H. Michael Habib, M.S. PhD. Candidate Center for Functional Anatomy and Evolution Johns Hopkins School of Medicine 1830 E. Monument Street Baltimore, MD 21205 (443) 280-0181 habib@jhmi.edu No virus found in this incoming message. Checked by AVG - http://www.avg.comVersion: 8.0.138 / Virus Database: 270.6.6/1627 - Release Date: 8/22/2008 6:48 AM



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